Reverberation circuit



Feb. 20,- 1934.

E. H. SCHREIBER REVERBERATION CIRCUIT Filed June 14, 1952 DIS CRIMI- N4TING NETWORK a i w LIM'LJ Dilly/[VG DEV/CE INVENTOR E H. SCHRE/BERATTORNEY 20' Several systems have Patented Feb. 20, 1934 1,947,621.navsannna'non cntcm'r Ernst H. Schreiber, Los Angeles, Calif., assignorto American Telephone and Telegraph Company, a-corporation of New YorkApplication June 14, 1932. Serial No. 611,201

2 Claims. 179-1) This invention relates to sound transmitting systemsand particularly to those employing a studio in which to initiate thesounds, such as radio broadcasting and phonograph recordin 5 systems.

One of the diilicultiesencountered in the transmission of sound from astudio is the lack of reverberation in the picked-up sound which oftenleads to inconsistencies between the sound and lo what the sound issuppos d to represent. It is impractical to use a separate room ior eachtype of program to be transmitted for the reverberation efiectssincesuch a scheme would require a great variety of rooms. Not only does thesine of a room ailectits reverberation characteristics.

but the nature of the walls and their sound re fleeting or absorbingqualitiesare alsoimportant factors tending to make this method stillless practical.

been devised to introduce reverberation into a. transmitting circuitartificially so that all types of sound can be picked up in the sameroom and yet be made to contain varying amounts systems usually take theform of a delay device of some kind, either acoustical or electrical,in-

sorted in the circuit between the transmitter and receiver. An exampleof the latter is disclosed in U. 8. Patent 1,647,242. to J. Mills,November 1. 1921, which shows a delay network used to simulatereverberation systems like this. though eiiective in producing an echo,do not take into account the selective frequency absorption of the wallsof aroom so that if it were desired to simulate the production of aprogram in a well-known auditorium, the frequency absorption characteristics of the studio would necessarily accompany the echocharacteristics of the auditorium. I

The object of'this invention is to provide an improved artificialreverberation circuit by means of which both the echo and the selectivefrequency absorption characteristics of a room or auditorium can besimulated.

reentrant loop circuit .in which a delay device, an amplifier, a.discriminating network and an attenuator are connected together inseries, with the main channel closing the loop. The attenuator isconnected to the main channel above the delay device so that the delayedcurrent is sent through the loop repeatedly until its energy "isexhausted Means are also provided for stabilizing the impedance ofvarious portions of the circuit to facilitate the adjustment of thecon-.

of reverberation. Such A simple form of the invention comprises a trolsto meet particular reverberation requirements.

The invention is illustrated by way. of example in the accompanyingdrawing. Apparatus wellknown in the art is not shown in detail, but isgo designated by rectangles and triangles for the sake o! simplicity andto make the invention more apparent.

A portion of the main channel is shown at 10 connected to an amplifier11 and continuing on through leads 12 to an output circuit. The sourceof sound-controlled electrical currents may be any form of sound pick-upand amplifying apparatus such as is used in broadcasting and-recordingstudios and is preferably taken as the 7 output of the mixing panel. Theamplifier 11 is 'of the conventional vacuum tube type and serves inaddition to augmenting the energy of a current as a means for causingthe current to flow unidirectionally. The outgoing current leaving 7 theamplifier 11 is divided in a suitable manner either by a potentiometer(not shown) across the leads, or by a resistance 18 in one of the leads.across thes'terminals of which the loop leads are connected. The currentthus diverted passes through resistancepad 14, the function of which isto stabilize the impedance of this portion of thecircuit; and then to adelay device 15. This delay device may be either acoustical, mechanicalor electrical, such as is disclosed, for example, in 1 U. 8. Patent No.1,647,242 to J. Mills. Prom the delay device 15 the current is againamplified in a conventional vacuum y 1 passes through a discriminatingfrequency net-' work 1'! where the frequency response characteristic ofthe system is shaped to conform to that of the roomto be simulated. .Thenetwork is made to terminate in a resistance pad 18 to stabilize itsaction. The amplifier 15 alsovserves to'maintain the flow of currentin'one direction only and to block any tendency to flow in the oppositedirection. The current then passes to an attenuator 19 which maintainsthe. strength of the delayed currents below that of the transmissionvline 10'to preventthe system from singing. Another resistance pad 20 isprovided through which the delay current reenters the transmission lineat the input side of amplifier 11. r

When the delayed currents have passed through amplifier 11 and reached-the resistance 13 they are again divided in the same proportion as werethe original currents, part of them passing on to the output 12 as thefirst reflection of the echo and thelremainder again passing through theloop where they are further delayed and attenuated to form the secondreflection of the echo. This continues until the energy of the echocurrent becomes negligible.

By selecting the proper time delay the echo produced in any sized roomcan be simulated. This echo can then be modified by thediscriminatingnetwork 17 to accentuate the frequencies generally foundto be most prominent in the room being simulated, and lastly, theoverall deadness of the room is simulated by the attenuator 19. 2 For along reverberation period the attenuation is somewhere near the point atwhich the system sings; for a short reverberation period the attenuationis greater and approaches the condition where no echo is produced. Anycondition'between these wide limits can be secured merely by adjustingthe attenuator.

The discriminating frequency network 1'7 is simply a series of filterscovering the entire band of frequencies being transmitted. The band maybe divided into as many small bands as desired with switching means formaking each band effective. .In this manner, certain frequencies can becut out of the echo to simulate the selective frequency absorption ofthe walls of a particular room. As explained above, the network is madeto terminate in a'resistance pad 18 to stabilize its action and todecrease the effects upon it of variations in the energy of the mainchannel, 1

The delay device 15 is adjustable to give ferent time delays. Theelectrical delay network shown in the U. S. Patent to J Mills, No.1,647,242, November 1, 1927, referred to above, may be used for thispurpose as well as the ordinary acoustic delay device comprising areceiver, a transmitter and an acoustic tube of variable lengthconnecting' the diaphragms of each. The latter, however,

may'not be compact enough or may not provide a 'suflicient variabilityto meet the requirements of the use to which it is put. A third form isone disclosed inU. S. patent to H. C. I-Iarrisomllo.

1,648,120, November 8, 1927, which comprises a mechanical counterpart ofthe Mills delay network. In any case, it is resirable to have the delaydevice variable and compact.

All of the apparatus used in this invention may be enclosed in a singlecontainer and can be readily connected into any transmission circuitwithout necessitating a change in existing studios and associatedpick-up apparatus. The reverberation period produced by it issusceptible of variation in both time and quality.

It is understood that the form shown and described is merelyillustrative of the invention and that various modifications of it canbe devised without departing from the scope of the invention as definedin the appended claims.

What is claimed is: v

1. In a main sound channel, apparatus comprising a loop circuit forintroducing reverberation effects into the main sound channel, andvariable and controllable means in the loop circuit for shaping thefrequency response characteristic of the loop circuit to simulate theselective frequency absorption of the walls of the room.

' 2: In a main sound channel for the transmission of ,sound-controlledelectrical currents, apparatusfor introducing reverberation effects intothe channel comprising a unidirectional amplifier connected into themain sound channel, means for dividing the output of the amplifier intoa plurality of channels, one of said channels comprising in series avariable acoustical delay device, an amplifier for the delayed currents,a discriminating network whereby certain 01 the frequencies transmittedtherethrough may be accentuated or attenuated, a variable attenuatorwhereby the rate of decay maybe regulated, and means for connecting theattenuator to the input of the unidirectional amplifier where in thedelayed currents are combined with the sound-controlled electricalcurrents of the main sound channel.

ERNST H.

